Bead Foam Compression Molding Method for Low Density Product

ABSTRACT

Disclosed is a method for molding a foamed article, such as a midsole or outsole for footwear, in which a desired amount of thermoplastic polyurethane foam beads are placed in a compression mold in the shape of the article and the mold is brought to a peak temperature of from about 130° C. to about 180° C. over a period of from about 300 to about 1500 seconds, then cooled to from about 5° C. to about 80° C. over a period of from about 300 to about 1500 seconds within about 30 seconds after the peak temperature is reached. The foamed article made by the method has a density of from about 0.1 to about 0.45 g/cm 3 .

FIELD OF THE INVENTION

The present invention relates to molding foamed articles, particularlyfor footwear.

INTRODUCTION TO THE DISCLOSURE

This section provides information helpful in understanding the inventionbut that is not necessarily prior art.

Thermoplastics are desirable as recyclable materials. However, thermosetmaterials can have properties better suited for some applications.

Brant et al., U.S. Pat. No. 6,759,443 describes polyurethane foam shoesoles made by foaming a polyurethane made from vinyl polymer-graftedpolyoxyalkylene polyether. Polyethylene wax and polytetrafluoroethyleneare added to improve abrasion resistance.

Takemura et al., U.S. Pat. No. 6,878,753 describes shoe soles andmidsoles made of a thermoset polyurethane foam. The foam is made by aprocess comprising mixing a polyol solution, which is previouslyprepared by mixing a polyol, with a catalyst, water and urea, a chainextender, and an additive as occasion demands, with a polyisocyanatecompound with stirring in a molding machine; and injecting the resultingmixture into a mold and foaming the mixture. The density of a moldedarticle of the polyurethane foam is said to be 0.15 to 0.45 g/cm³.

Fischer et al., WO 94/20568, describes thermoplastic polyurethanemini-pellet or bead foams with an average diameter of 1-20 millimeters.The polyurethanes are polyester- and polyether-based materials. The beadfoams are molded under pressure and heated by introducing pressurizedsteam.

Prissok et al, US Patent Application Publication No. 2010/0047550describes a hybrid material with a matrix of polyurethane and foamedparticles of thermoplastic polyurethane embedded in the matrix. Thehybrid material may be used for making shoe soles. The matrixpolyurethane may be foamed during molding.

Prissok et al., US Patent Application Publication No. 2010/0222442describes an expandable thermoplastic polyurethane including a blowingagent and having a Shore hardness of A 44 to A 84. Foams can be producedfrom expanded beads of the polyurethane by fusing them to one another ina closed mold with exposure to heat. Prissok et al. teach that the beadsare charged to the mold, the mold is closed, and steam or hot air isintroduced into the mold to further expand the beads and fuse themtogether. A foam made in this way is said to have a density in the rangeof from 8 to 600 g/L.

It has been found, however, that prior methods of molding foamed beadsor minipellets can cause the beads to partially compress, which isundesirable in applications where lower density is desirable.

SUMMARY OF THE DISCLOSURE

This section provides a general summary rather than a comprehensivedisclosure of the full scope of the invention and of all its features.

Disclosed is a method for molding a foamed article, such as a midsolefor footwear, in which a desired amount of thermoplastic polyurethanefoam beads are placed in a compression mold in the shape of the articleand the mold is brought to a peak temperature of from about 130° C. toabout 180° C. over a period of from about 300 to about 1500 seconds,then cooled to from about 5° C. to about 80° C. over a period of fromabout 300 to about 1500 seconds within about 30 seconds after the peaktemperature is reached. The foam beads may have a density of from about0.01 to about 0.3 g/cm³ and the molded article may have a density fromabout 0.1 to about 0.45 g/cm³.

The method may be used to make a component for an article of footwearsuch as a midsole, a component of a midsole such as a cushioning pad, ora sockliner.

“A,” “an,” “the,” “at least one,” and “one or more” are usedinterchangeably to indicate that at least one of the item is present; aplurality of such items may be present unless the context clearlyindicates otherwise. All numerical values of parameters (e.g., ofquantities or conditions) in this specification, including the appendedclaims, are to be understood as being modified in all instances by theterm “about” whether or not “about” actually appears before thenumerical value. “About” indicates that the stated numerical valueallows some slight imprecision (with some approach to exactness in thevalue; approximately or reasonably close to the value; nearly). If theimprecision provided by “about” is not otherwise understood in the artwith this ordinary meaning, then “about” as used herein indicates atleast variations that may arise from ordinary methods of measuring andusing such parameters. In addition, disclosure of ranges includesdisclosure of all values and further divided ranges within the entirerange.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawing is illustrates a selected embodiment described in thepresent disclosure.

The FIGURE shows a flowchart of a method for molding thermoplasticpolyurethane foam beads into an article, such as a component for anarticle of footwear.

DETAILED DESCRIPTION

A detailed description of exemplary, nonlimiting embodiments follows.

The thermoplastic polyurethane foam mini-pellets or beads may have adensity of from about 0.01 to about 0.3 g/cm³. In general, a lowerdensity for the thermoplastic polyurethane foam beads allows a lowerdensity for a product molded from the beads. In various embodiments, thefoam beads may have a density equal to or less than about 0.3 g/cm³ orequal to or less than about 0.1 g/cm³. For example, the thermoplasticpolyurethane foam beads may have a density of from about 0.03 to about0.1 g/cm³. The thermoplastic polyurethane foam beads are prepared from athermoplastic polyurethane. The beads may be prepared using solely onethermoplastic polyurethane or may be prepared from a polymer blend oftwo or more thermoplastic polyurethanes. The beads may be integralfoams.

The thermoplastic polyurethane from which the foam beads are preparedmay have a melt index (also called a melt flow index or melt flow rate)of at least about 160 grams/10 min. (at 190° C., 21.6 kg) as measuredaccording to ASTM D1238. In various embodiments, the melt index may befrom about 160 to about 250 grams/10 min. (at 190° C., 21.6 kg) or fromabout 160 to about 220 grams/10 min. (at 190° C., 21.6 kg), in each caseas measured according to ASTM D1238.

Thermoplastic polyurethanes can be produced via reaction of (a)diisocyanates with difunctional compounds reactive toward isocyanates.In general, the difunctional compounds have two hydroxyl groups (diols)and may have a molar mass of from 62 (the molar mass of ethylene glycol)to about 10,000, although difunctional compounds having otherisocyanate-groups (e.g., secondary amine) may be used, generally inminor amounts, and a limited molar fraction of tri-functional andmono-functional isocyanate-reactive compounds may be used. Preferably,the polyurethane is linear. Including difunctional compounds with molarmasses of about 400 or greater introduces soft segments into thepolyurethane. An increased ratio of soft segments to hard segments inthe polyurethane causes the polyurethane to become increasingly moreflexible and eventually elastomeric. In certain embodiments, such aswhen the molded article is an outsole for an article of footwear, thebeads may advantageously be prepared using a rigid thermoplasticpolyurethane or combination of thermoplastic polyurethanes. In variousother embodiments, such as when the molded article is a midsole forfootwear, the beads may advantageously be prepared using an elastomericthermoplastic polyurethane or a combination of elastomeric thermoplasticpolyurethanes.

Suitable elastomeric thermoplastic polyurethanes include thermoplasticpolyester-polyurethanes, polyether-polyurethanes, andpolycarbonate-polyurethanes. Nonlimiting, suitable examples of theseinclude, without limitation, polyurethanes polymerized using as diolreactants polyesters diols prepared from diols and dicarboxylic acids oranhydrides, polylactone polyesters diols (for example polycaprolactonediols), polyester diols prepared from hydroxy acids that aremonocarboxylic acids containing one hydroxyl group, polytetrahydrofurandiols, polyether diols prepared from ethylene oxide, propylene oxide, orcombinations of ethylene oxide and propylene oxide, and polycarbonatediols such as polyhexamethylene carbonate diol andpoly(hexamethylene-co-pentamethylene) carbonate diols. The elastomericthermoplastic polyurethane may be prepared by reaction of one of thesepolymeric diols (polyester diol, polyether diol, polylactone diol,polytetrahydrofuran diol, or polycarbonate diol), one or morepolyisocyanates, and, optionally, one or more monomeric chain extensioncompounds. Chain extension compounds are compounds having two or morefunctional groups, preferably two functional groups, reactive withisocyanate groups. Preferably the elastomeric thermoplastic polyurethaneis substantially linear (i.e., substantially all of the reactants aredi-functional).

Nonlimiting examples of polyester diols used in forming the elastomericthermoplastic polyurethane include those prepared by the condensationpolymerization of dicarboxylic compounds, their anhydrides, and theirpolymerizable esters (e.g. methyl esters) and diol compounds.Preferably, all of the reactants are di-functional, although smallamounts of mono-functional, tri-functional, and higher functionalitymaterials (perhaps up to a few mole percent) can be included. Suitabledicarboxylic acids include, without limitation, glutaric acid, succinicacid, malonic acid, oxalic acid, phthalic acid, hexahydrophthalic acid,adipic acid, maleic acid, anhydrides of these, and mixtures thereof.Suitable polyols include, without limitation, wherein the extender isselected from the group consisting of ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, propylene glycol,dipropylene glycol, tripropylene glycol, tetrapropylene glycol,cyclohexanedimethanol, 2-ethyl-1,6-hexanediol, 1,4-butanediol,1,5-pentanediol, 1,3-propanediol, butylene glycol, neopentyl glycol, andcombinations thereof. Small amounts of triols or higher functionalitypolyols, such as trimethylolpropane or pentaerythritol, are sometimesincluded. In a preferred embodiment, the carboxylic acid includes adipicacid and the diol includes 1,4-butanediol. Typical catalysts for theesterification polymerization are protonic acids, Lewis acids, titaniumalkoxides, and dialkyl tin oxides.

Hydroxy carboxylic acid compounds such as 12-hydroxy stearic acid mayalso be polymerized to produce a polyester diol. Such a reaction may becarried out with or without an initiating diol such as one of the diolsalready mentioned.

Polylactone diol reactants may also be used in preparing the elastomericthermoplastic polyurethanes. The polylactone diols may be prepared byreacting a diol initiator, e.g., a diol such as ethylene or propyleneglycol or another of the diols already mentioned, with a lactone.Lactones that can be ring opened by an active hydrogen such as, withoutlimitation, ε-caprolactone, γ-caprolactone, β-butyrolactone,β-propriolactone, γ-butyrolactone, α-methyl-γ-butyrolactone,β-methyl-γ-butyrolactone, γ-valerolactone, δ-valerolactone,γ-decanolactone, δ-decanolactone, γ-nonanoic lactone, γ-octanoiclactone, and combinations of these can be polymerized. The lactone ringcan be substituted with alkyl groups of 1-7 carbon atoms. In onepreferred embodiment, the lactone is E-caprolactone. Useful catalystsinclude those mentioned above for polyester synthesis. Alternatively,the reaction can be initiated by forming a sodium salt of the hydroxylgroup on the molecules that will react with the lactone ring.

In preparing a polyether diol, a diol initiator such as ethylene glycol,propylene glycol, 1,4-butanediol, or another of the diols mentionedabove is reacted with an oxirane-containing compound to produce apolyether diol. The oxirane-containing compound is preferably analkylene oxide or cyclic ether, and more preferably it is a compoundselected from ethylene oxide, propylene oxide, 1-butene oxide,tetrahydrofuran, and combinations of these. Other useful cyclic ethersthat may be polymerized include, without limitation, 1,2-cyclohexeneoxide, 2-butene oxide, 1-hexene oxide, tert-butylethylene oxide, phenylglycidyl ether, 1-decene oxide, isobutylene oxide, cyclopentene oxide,1-pentene oxide, and combinations of these. The polyether polymerizationis typically base-catalyzed. The polymerization may be carried out, forexample, by charging the hydroxyl-functional initiator and a catalyticamount of caustic, such as potassium hydroxide, sodium methoxide, orpotassium tert-butoxide, and adding the alkylene oxide at a sufficientrate to keep the monomer available for reaction. Two or more differentalkylene oxide monomers may be randomly copolymerized by coincidentaladdition and polymerized in blocks by sequential addition.

Tetrahydrofuran may be polymerized by a cationic ring-opening reactionusing such counterions as SbF₆ ⁻, AsF₆ ⁻, PF₆ ⁻, SbCl₆ ⁻, BF₄ ⁻, CF₃SO₃⁻, FSO₃ ⁻, and ClO₄ ⁻. Initiation is by formation of a tertiary oxoniumion. The polytetrahydrofuran segment can be prepared as a “livingpolymer” and terminated by reaction with the hydroxyl group of a diolsuch as any of those mentioned above.

Aliphatic polycarbonates may be prepared by polycondensation ofaliphatic diols with dialkyl carbonates, (such as diethyl carbonate),cyclic glycol carbonates (such as cyclic carbonates having five- andsix-member rings), or diphenyl carbonate, in the presence of catalystslike alkali metal, tin catalysts, or titanium compounds. or diphenylcarbonate. Another way to make aliphatic polycarbonates is byring-opening polymerization of cyclic aliphatic carbonates catalyzed byorganometallic catalysts. The polycarbonate diols can also be made bycopolymerization of epoxides with carbon dioxide. Aliphaticpolycarbonate diols are prepared by the reaction of diols with dialkylcarbonates (such as diethyl carbonate), diphenyl carbonate, ordioxolanones (such as cyclic carbonates having five- and six-memberrings) in the presence of catalysts like alkali metal, tin catalysts, ortitanium compounds. Useful diols include, without limitation, any ofthose already mentioned. Aromatic polycarbonates are usually preparedfrom reaction of bisphenols, e.g., bisphenol A, with phosgene ordiphenyl carbonate.

The polymeric diol, such as the polymeric polyester diols and polyetherdiols described above, that are used in making an elastomericthermoplastic polyurethane synthesis preferably have a number averagemolecular weight (determined for example by the ASTM D-4274 method) offrom about 300 to about 8,000, or from about 300 to about 5000, or fromabout 300 to about 3000.

The synthesis of a elastomeric thermoplastic polyurethane may be carriedout by reacting one or more of the polymeric diols, one or morecompounds having at least two (preferably two) isocyanate groups, and,optionally, one or more chain extension agents. The elastomericthermoplastic polyurethanes are preferably linear and thus thepolyisocyanate component preferably is substantially di-functional.Useful diisocyanate compounds used to prepare the elastomericthermoplastic polyurethanes, include, without limitation, methylenebis-4-cyclohexyl isocyanate, cyclohexylene diisocyanate (CHDI),isophorone diisocyanate (IPDI), m-tetramethyl xylylene diisocyanate(m-TMXDI), p-tetramethyl xylylene diisocyanate (p-TMXDI), ethylenediisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane,1,6-diisocyanatohexane (hexamethylene diisocyanate or HDI), 1,4-butylenediisocyanate, lysine diisocyanate, 1,4-methylene bis-(cyclohexylisocyanate), 2,4-tolylene (“toluene”) diisocyanate and 2,6-tolylenediisocyanate (TDI), 2,4′-methylene diphenyl diisocyanate (MDI),4,4′-methylene diphenyl diisocyanate (MDI), o-, m-, and p-xylylenediisocyanate (XDI), 4-chloro-1,3-phenylene diisocyanate, naphthylenediisocyanates including 1,2-naphthylene diisocyanate, 1,3-naphthylenediisocyanate, 1,4-naphthylene diisocyanate, 1,5-naphthylenediisocyanate, and 2,6-naphthylene diisocyanate, 4,4′-dibenzyldiisocyanate, 4,5′-diphenyldiisocyanate, 4,4′-diisocyanatodibenzyl,3,3′-dimethoxy-4,4′-biphenylene diisocyanate,3,3′-dimethyl-4,4′-biphenylene diisocyanate, 1,3-diisocyanatobenzene,1,4-diisocyanatobenzene, and combinations thereof. Particularly usefulis diphenylmethane diisocyanate (MDI).

Useful active hydrogen-containing chain extension agents generallycontain at least two active hydrogen groups, for example, diols,dithiols, diamines, or compounds having a mixture of hydroxyl, thiol,and amine groups, such as alkanolamines, aminoalkyl mercaptans, andhydroxyalkyl mercaptans, among others. The molecular weight of the chainextenders may range from about 60 to about 400 g/mol. Alcohols andamines are preferred in some embodiments. Typical examples of usefuldiols that are used as polyurethane chain extenders include, withoutlimitation, 1,6-hexanediol, cyclohexanedimethanol (sold as CHDM byEastman Chemical Co.), 2-ethyl-1,6-hexanediol, 1,4-butanediol, ethyleneglycol and lower oligomers of ethylene glycol including diethyleneglycol, triethylene glycol and tetraethylene glycol; propylene glycoland lower oligomers of propylene glycol including dipropylene glycol,tripropylene glycol and tetrapropylene glycol; 1,3-propanediol,neopentyl glycol, dihydroxyalkylated aromatic compounds such as thebis(2-hydroxyethyl)ethers of hydroquinone and resorcinol;p-xylene-α,α′-diol; the bis(2-hydroxyethyl)ether of p-xylene-α,α′-diol;m-xylene-α,α′-diol and the bis(2-hydroxyethyl)ether;3-hydroxy-2,2-dimethylpropyl 3-hydroxy-2,2-dimethylpropanoate; andmixtures thereof. Suitable diamine extenders include, withoutlimitation, p-phenylenediamine, m-phenylenediamine, benzidine,4,4′-methylenedianiline, 4,4′-methylenibis (2-chloroaniline), ethylenediamine, and combinations of these. Other typical chain extenders areamino alcohols such as ethanolamine, propanolamine, butanolamine, andcombinations of these. Preferred extenders include ethylene glycol,diethylene glycol, triethylene glycol, tetraethylene glycol, propyleneglycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol,1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, and combinationsof these.

In addition to the above-described di-functional extenders, a smallamount of tri-functional extenders such as trimethylolpropane,1,2,6-hexanetriol and glycerol, and/or mono-functional active hydrogencompounds such as butanol or dimethyl amine, may also be present. Theamount of tri-functional extenders and/or mono-functional compoundsemployed would preferably be a few equivalent percent or less based onthe total weight of the reaction product and active hydrogen containinggroups employed.

The reaction of the polyisocyanate(s), polymeric diol(s), and,optionally, chain extension agent(s) is typically conducted by heatingthe components, generally in the presence of a catalyst. Typicalcatalysts for this reaction include organotin catalysts such as stannousoctoate or dibutyl tin dilaurate. Generally, the ratio of polymericdiol, such as polyester diol, to extender can be varied within arelatively wide range depending largely on the desired hardness of theelastomeric thermoplastic polyurethane. For example, the equivalentproportion of polyester diol to extender may be within the range of 1:0to 1:12 and, more preferably, from 1:1 to 1:8. Preferably, thediisocyanate(s) employed are proportioned such that the overall ratio ofequivalents of isocyanate to equivalents of active hydrogen containingmaterials is within the range of 0.95:1 to 1.10:1, and more preferably,0.98:1 to 1.04:1. The polymeric diol segments typically are from about25% to about 65% by weight of the elastomeric thermoplasticpolyurethane, and preferably from about 25% to about 50% by weight ofthe elastomeric thermoplastic polyurethane.

One nonlimiting example of commercially available elastomericthermoplastic polyurethanes having a melt flow index of from about 160to about 220 grams/10 min. (at 190° C., 21.6 kg) suitable for making thethermoplastic polyurethane foam beads is Elastollan® SP9213 (melt flowindex of 200 g/10 min. (at 190° C., 21.6 kg)), which is available fromBASF Polyurethanes GmbH.

A thermoplastic polyurethane that is more rigid may be synthesized inthe same way but with a lower content of the polymeric diol segments. Arigid thermoplastic polyurethane may, for example, include from about 0to about 25 percent by weight of the polyester, polyether, orpolycarbonate diol segments. Synthesis of rigid polyurethanes iswell-known in the art and described in many references. Rigidthermoplastic polyurethanes having a melt index of at least about 160grams/10 min. (at 190° C., 21.6 kg) as measured according to ASTM D1238are commercially available and include those sold under the trademarkIsoplast® ETPU by Lubrizol Corp., Wickliffe, Ohio.

The thermoplastic polyurethane foam beads may be made from theelastomeric thermoplastic polyurethane by a method as disclosed inFischer et al., WO 94/20568 and Prissok et al, US Patent ApplicationPublications No. US 2010/0222442 and 2010/0047550, each of which areincorporated herein in its entirety by reference. The flexiblepolyurethane foams made by such a process preferably have a proportionof open cells in accordance with DIN ISO 4590 of greater than 85%,particularly preferably greater than 90%.

The thermoplastic polyurethane foam beads may have a broad range ofshapes, including generally spherical, cylindrical ellipsoidal, cubic,rectangular, and other generally polyhedral shapes as well as irregularor other shapes, including those having circular, elliptical, square,rectangular or other polygonal cross-sectional outer perimeter shapes orirregular cross-sectional shapes with or without uniform widths ordiameters along an axis. “Generally” is used here to indicate an overallshape that may have imperfections and irregularities, such as bumps,dents, imperfectly aligned edges, corners, or sides, and so on. Invarious embodiments, the thermoplastic polyurethane foam beads maypreferably be generally spherical or ellipsoidal. In the case ofnon-spherical beads, for example ellipsoidal beads, the largest majordiameter of a cross-section taken perpendicular to the major (longest)axis of the ellipsoid. The thermoplastic polyurethane foam beads maypreferably have a diameter of from about 0.5 mm to about 1.5 cm.Ellipsoidal beads may be from about 2 mm to about 20 mm in length andfrom about 1 to about 20 mm in diameter. Each individual bead may be,for example, from about 20 to about 45 mg in weight. The foamedparticles preferably have a compact outer skin. Here, reference to acompact skin means that the foam cells in the outer region of the foamedparticles are smaller than those in the interior. Particular preferenceis given to the outer region of the foamed particles having no pores.

Referring now to the FIGURE, a process 10 of preparing a molded articlefrom thermoplastic polyurethane foam beads has a step 12 in which adesired amount of the thermoplastic polyurethane foam beads are placedin the compression mold. The foamed beads may be placed in the mold whenboth the mold and the foamed beads are at a temperature below about 80°C. Preferably, the temperatures of the mold and of the foamed beads areboth ambient temperature (about 5-27° C.), although as mentioned thetemperatures of each may be higher, up to perhaps 80° C. In step 14 themold is closed. Once the mold is closed a locking pin may be inserted tokeep the mold closed. With the mold closed it can be heated, e.g. byshuttling the mold to the hot side of the press. A minimum pressure toclose (and keep closed) the mold may depend, for example, on the moldsurface area and volume of beads being compressed in the mold cavity.The quantity of beads inserted into the mold can be changed to vary thedensity of the molded product. As a nonlimiting example, 70 grams ofbeads may be molded in a mold with a volume of 175 cm³ to provide amolded article with a density of 0.25 g/cm³, while 100 grams of the samebeads may be molded in the mold with the volume of 175 cm³ to provide amolded article with a density of 0.3 g/cm³.

In step 16, the mold is brought to a peak temperature that is in therange of from about 130° C. to about 180° C. over a period of from about300 to about 1500 seconds. In general, a longer time may be used forheating a thicker part to mold the part. Thus, a thicker part may bebrought to the peak molding temperature over a longer period of timecompared to the time in which a thinner part is brought to the peakmolding temperature. In various embodiments, the peak moldingtemperature is in the range of from about 140° C. to about 170° C. Invarious embodiments, the mold is brought to the peak temperature over aperiod of from about 300 to about 1200 seconds or from about 300 toabout 900 seconds. A desired skin thickness may be achieved by selectionof the maximum heating temperature within the temperature range. Skinthickness may be selected to alter cushioning and feel of a moldedmidsole as used in an article of footwear. The skin thickness on a beadmay be about 10 micrometers. The skin thickness on a molded part may beat least about 20 micrometers. A molding temperature of about 130° C.produces a thinner skin than does a molding temperature of about 180° C.In various embodiments, the peak temperature is selected to produce askin thickness of from about 10 to about 200 micrometers.

In step 18 the mold is then cooled to a temperature of from about 5° C.to about 80° C. over a period of from about 300 to about 1500 seconds.Cooling is typically carried out by moving the mold to the cold side ofthe compression molding press between two cold plates. In general, alonger time may be used for cooling a thicker part. Thus, a thicker partmay be cooled over a longer period of time compared to the time in whicha thinner part is cooled to the same temperature. In variousembodiments, the part may be cooled over a period of from about 300 toabout 1200 seconds or over a period of from about 300 to about 900seconds. In various embodiments, the cooling step 18 is begun as soon asa peak temperature is reached in step 16. The cooling step 18 may bebegun within 30 seconds, or within 10 seconds, or from about 0 to about5 seconds, or immediately after the peak temperature is reached in step16. The mold and molded article may be cooled a rate of from about 0.09to about 0.55° C./second. A rate of cooling in this range avoidsshrinking of the molded article so that the article has a lower densitythan if not cooled at a rate in this range.

In step 20 the molded article is removed from the mold.

The molded article may have a density of less than about 0.45 g/cm³,preferably less than about 0.4 g/cm³, more preferably less than about0.35 g/cm³. In various embodiments, the molded article may have adensity of from about 0.1 to about 0.45 g/cm³, or a density of fromabout 0.1 to about 0.4 g/cm³, or a density of from about 0.1 to about0.35 g/cm³.

The articles molded by the disclosed process have lower densities ascompared to articles molded from the thermoplastic polyurethane foambeads using steam to heat the mold contents. While hot air could also beused to heat the thermoplastic polyurethane foam beads in a mold,heating with hot air would take substantially longer because the heattransfer with hot air is substantially slower.

The molded article also has better definition of character lines ormolded-in designs as compared to articles molded from the thermoplasticpolyurethane foam beads using steam to heat the mold contents. Examplesof character lines and designs are letters, symbols, undercuts, and bitelines. Such character lines may have depths of from about 0.1 cm toabout 10 cm.

The molded article may be incorporated as cushioning into otherarticles. As nonlimiting examples, the molded article may be a foamelement in footwear, such as a part of a footwear upper, such as a foamelement in a collar, a midsole or a part of a midsole, or an outsole ora part of an outsole; foam padding in shinguards, shoulder pads, chestprotectors, masks, helmets or other headgear, knee protectors, and otherprotective equipment; an element placed in an article of clothingbetween textile layers; or may be used for other known paddingapplications for protection or comfort, especially those for whichweight of the padding is a concern.

In various embodiments, the molded article is a midsole for an articleof footwear. A midsole provides cushioning in the footwear. A midsoleshould be durable but also preferably adds as little weight as possibleto the footwear while still cushioning to the desired degree. A midsolealso should be able to be bonded to an outsole, an upper, or any othercomponents (e.g., a shank, an airbag, or decorative components) inmaking an article of footwear.

In other embodiments, the molded article is an outsole for an article offootwear. An outsole may be molded using thermoplastic polyurethane foambeads made with a rigid thermoplastic polyurethane.

The invention is further described in the following examples. Theexamples are merely illustrative of various embodiments. All parts areparts by weight unless otherwise noted.

Examples 1-3 of the Invention

In each of Examples 1-3, a compression mold fitted with a mold for afootwear midsole was filed with an amount as shown in Table 1 ofthermoplastic polyurethane foam beads obtained from BASF Corporation,Wyandotte, Mich. (10 mm in length ±2 mm, diameter of 0.5 mm±0.2 mm,density of 0.28 to 0.3 g/cm³). The mold was closed, and the mold wasthen heated from about 18-22° C. to a temperature of 160° C. in 600seconds between hot plates. The mold was immediately cooled to atemperature of 8° C. over a period of 600 seconds between cold plates.The molded midsole was removed from the mold for measurements. Densityand resiliency were measured for each of the three midsole examples 1-3molded in this way, and the values are recorded in Table 1.

TABLE 1 Bead Density Resiliency, % Mass g/cm³ (ASTM D2632) Example 1  75g 0.214 56 Example 2 116 g 0.331 61 Example 3 117 g 0.334 60

Examples 4 and 5 of the Invention

In each of Examples 4 and 5, a compression mold fitted with a mold for arectangular slab with a thickness of 20 mm was filed with an amount asshown in Table 2 of thermoplastic polyurethane foam beads like thoseused in Examples 1-3. The mold was closed, and the mold was then heatedbetween hot plates from about 18-22° C. over a period of time and to atemperature as shown in Table 2. The mold was immediately cooled to atemperature of 8° C. over a period of 600 seconds between cold plates.The molded slabs were removed from the mold for measurements. Densitywas measured for each of the midsole examples molded in this way, andthe values are recorded in Table 2.

TABLE 2 Bead Density, Mass Heating Cycle g/cm³ Example 4 70 g heated to165° C. 0.230 in 900 sec. Example 5 60 g heated to 165° C. 0.190 in 900sec.

Comparative Example

A comparative example was prepared using steam heating as disclosed inPrissok et al., US Patent Application Publication No. 2010/0222442. Inthis example, the beads like those used in Examples 1-3 were place in acompression mold fitted with a midsole mold as in Examples 1-3 and themold was closed. The beads were heated using steam injected into themold from room temperature (about 22° C.) to about 120° C. in 1-2minutes, then cooled to about 22° C. in about 2-3 minutes. The densityof the molded midsole was 0.35 g/cm³.

The examples show that a molded midsole article with a density of fromabout 0.10 to 0.45 g/cm³ from bead foams according to the process nowdisclosed provides resiliency from about 45-65% as tested by ASTM D2632.As compared to the steam-molded part of the Comparative Example, theExamples 4 and 5 of the invention had lower densities and betterdefinition of character lines and designs molded into the surfaces.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

1. A method for molding a foamed article, comprising: placing a desiredamount of thermoplastic polyurethane foam beads in a compression mold inthe shape of an article, wherein the thermoplastic polyurethane foambeads have a density of from about 0.01 to about 0.3 g/cm³; closing themold; bringing the mold to a peak temperature of from about 130° C. toabout 180° C. over a period of from about 300 to about 1500 seconds;cooling the mold to a temperature of from about 5° C. to about 80° C.over a period of from about 300 to about 1500 seconds within about 30seconds after the peak temperature is reached; and removing the article.2. A method according to claim 1, wherein the peak mold temperature isfrom about 140° C. to about 170° C.
 3. A method according to claim 1,wherein the thermoplastic polyurethane foam beads have a density of fromabout 0.01 to about 0.1 g/cm³.
 4. A method according to claim 1, whereinthe thermoplastic polyurethane foam beads comprise a thermoplasticpolyurethane with a melt flow index of at least about 160 grams/10 min.(at 190° C., 21.6 kg) as measured according to ASTM D1238.
 5. A methodaccording to claim 1, wherein the thermoplastic polyurethane foam beadscomprise an elastomeric thermoplastic polyurethane with a melt flowindex of from about 180 to about 250 grams/10 min. (at 190° C., 21.6 kg)as measured according to ASTM D1238.
 6. A method according to claim 1,wherein the thermoplastic polyurethane foam beads comprise anelastomeric thermoplastic polyurethane selected from the groupconsisting of thermoplastic polyester-polyurethanes,polyether-polyurethanes, and polycarbonate-polyurethanes.
 7. A methodaccording to claim 1, wherein the thermoplastic polyurethane foam beadscomprise elastomeric thermoplastic polyester-polyurethane.
 8. A methodaccording to claim 1, wherein the thermoplastic polyurethane foam beadscomprise an elastomeric thermoplastic polyether-polyurethane.
 9. Amethod according to claim 8, wherein the elastomeric thermoplasticpolyether-polyurethane is a reaction product of diphenylmethanediisocyanate.
 10. A method according to claim 1, wherein thethermoplastic polyurethane foam beads have a diameter of from about 0.5mm to about 1.5 cm.
 11. A method according to claim 1, wherein thethermoplastic polyurethane foam beads have a compact outer skin.
 12. Amethod according to claim 1, wherein the thermoplastic polyurethane foambeads and the mold are each at a temperature below about 80° C.
 13. Amethod according to claim 1, wherein the amount of the thermoplasticpolyurethane foam beads placed in the mold is selected to provide afoamed article having a density of from about 0.1 to about 0.45 g/cm³.14. A method according to claim 1, wherein the mold is brought to thepeak temperature over a period of from about 300 to about 1200 seconds.15. A method according to claim 1, wherein the peak temperature isselected to produce a skin thickness of from about 9 to about 200micrometers.
 16. A method according to claim 1, wherein the mold iscooled over a period of from about 300 to about 1200 seconds.
 17. Amethod according to claim 1, wherein the mold cooling step is begunimmediately after the peak temperature is reached.
 18. A methodaccording to claim 1, wherein the mold is cooled at a rate of from about0.09 to about 0.55° C./second.
 19. An article prepared by the methodaccording to claim
 1. 20. An article according to claim 19, wherein thearticle is a midsole, a cushioning pad, a sockliner, or an outsole forfootwear.
 21. An article according to claim 19, wherein the article hasa molded-in character line or design.